Overall score for the 3M Filtrete 600 Dust & Pollen is mainly how well the model removed dust and smoke from a test chamber, plus quietness for room purifiers and airflow resistance for whole-house units.
Dust/pollen/smoke removal: How well models cleared air of fine clay dust and cigarette smoke. Ones that scored well for dust removal should perform comparably for pollen. Airflow resistance: How freely air passes through a whole-house unit.